1. Field of the Invention
The invention relates to a system and method of shipboard regasification of liquefied natural gas (“LNG”). Particularly, this system and method relates to dockside ship-to-ship transfer of LNG in connection with the shipboard regasification of LNG.
2. Description of the Related Art
Natural gas is often carried onboard special cryogenic tanker ships from the location of its origin to the location of consumption. In this way, natural gas may be transported to areas with a higher demand for natural gas. Since LNG occupies only about 1/600th of the volume that the same amount of natural gas does in its gaseous state, liquefying the natural gas for transport facilitates the transportation process and improves the economics of the system. LNG is produced in onshore liquefaction plants by cooling natural gas below its boiling point (−259° F. at ambient pressures). The LNG may be stored in cryogenic containers either at or slightly above atmospheric pressure. Typically, the LNG will be regasified prior to its distribution to end users. Regasification may be accomplished by raising the temperature of the LNG at a regasification facility, which may be located onboard a mobile vessel. There are various methods for vaporizing the LNG onboard a vessel. In these methods, heat from at least one heat source, such as seawater, air, or steam from the ship's auxiliary boilers, is transferred to the LNG through heat exchangers which allows the LNG to be vaporized.
Traditionally, a mobile vessel equipped with regasification facilities is loaded with LNG cargoes at the natural gas supply source and travels across the ocean to another location for offloading and distribution. In another example, a vessel with regasification facilities is loaded with LNG cargoes using ship-to-ship (STS) transfer of LNG upstream of the receiving port at a location between the LNG load port and the delivery port. In such an example, a conventional LNG carrier collects the LNG from the natural gas supply source and is used for the long haul transportation. The conventional LNG carrier delivers the cargos from the supply source to the STS transfer location. The regasification vessel is used in shuttle service between the STS transfer location and the offloading port. In these examples, the offloading of natural gas is disturbed since the LNG carrier with regasification facilities must leave the offloading location to receive additional LNG cargoes, which is undesirable.
It has also been proposed that a conventional LNG carrier berth along side a floating platform for the onboard regasification of LNG that is attached to a riser, and the riser is connected to the sea bottom at a location where an underwater pipeline exists. For example, a regasification unit may discharge natural gas to an underwater pipeline using a sub-sea riser and connector such as a turret. However, constructing such a facility is costly and time consuming and locations having underwater pipelines are limited. As a result, such an arrangement is not suitable for many locations in need of a timely natural gas supply at a low cost.